Buggy code:
@ SuppressWarnings ( "deprecation" ) public class StringUtilsTest { static final String WHITESPACE ; static final String NON_WHITESPACE ; static final String HARD_SPACE ; static final String TRIMMABLE ; static final String NON_TRIMMABLE ; private static final String [ ] ARRAY_LIST = new String [ ] { "foo" , "bar" , "baz" } ; private static final String [ ] EMPTY_ARRAY_LIST = new String [ ] { } ; private static final String [ ] NULL_ARRAY_LIST = new String [ ] { null } ; private static final Object [ ] NULL_TO_STRING_LIST = new Object [ ] { new Object ( ) { @ Override public String toString ( ) { } } } ; private static final String [ ] MIXED_ARRAY_LIST = new String [ ] { null , "" , "foo" } ; private static final Object [ ] MIXED_TYPE_LIST = new Object [ ] { "foo" , Long . valueOf ( 2L ) } ; private static final long [ ] LONG_PRIM_LIST = new long [ ] { 1 , 2 } ; private static final int [ ] INT_PRIM_LIST = new int [ ] { 1 , 2 } ; private static final byte [ ] BYTE_PRIM_LIST = new byte [ ] { 1 , 2 } ; private static final short [ ] SHORT_PRIM_LIST = new short [ ] { 1 , 2 } ; private static final char [ ] CHAR_PRIM_LIST = new char [ ] { '1' , '2' } ; private static final float [ ] FLOAT_PRIM_LIST = new float [ ] { 1 , 2 } ; private static final double [ ] DOUBLE_PRIM_LIST = new double [ ] { 1 , 2 } ; private static final String SEPARATOR = "," ; private static final char SEPARATOR_CHAR = ';' ; private static final String TEXT_LIST = "foo,bar,baz" ; private static final String TEXT_LIST_CHAR = "foo;bar;baz" ; private static final String TEXT_LIST_NOSEP = "foobarbaz" ; private static final String FOO_UNCAP = "foo" ; private static final String FOO_CAP = "Foo" ; private static final String SENTENCE_UNCAP = "foo<seq2seq4repair_space>bar<seq2seq4repair_space>baz" ; private static final String SENTENCE_CAP = "Foo<seq2seq4repair_space>Bar<seq2seq4repair_space>Baz" ; @ Test public void testConstructor ( ) { } @ Test public void testIsEmpty ( ) { } @ Test public void testIsNotEmpty ( ) { } @ Test public void testIsAnyEmpty ( ) { } @ Test public void testIsNoneEmpty ( ) { } @ Test public void testIsBlank ( ) { } @ Test public void testIsNotBlank ( ) { } @ Test public void testIsAnyBlank ( ) { } @ Test public void testIsNoneBlank ( ) { } @ Test public void testCaseFunctions ( ) { } @ Test public void testSwapCase_String ( ) { } @ Test public void testJoin_Objects ( ) { } @ Test public void testJoin_Objectarray ( ) { assertNull ( StringUtils . join ( ( ( Object [ ] ) ( null ) ) ) ) ; <START_BUG> assertEquals ( "" , StringUtils . join ( ) ) ; <END_BUG> assertEquals ( "" , StringUtils . join ( ( ( Object ) ( null ) ) ) ) ; assertEquals ( "" , StringUtils . join ( StringUtilsTest . EMPTY_ARRAY_LIST ) ) ; assertEquals ( "" , StringUtils . join ( StringUtilsTest . NULL_ARRAY_LIST ) ) ; assertEquals ( "null" , StringUtils . join ( StringUtilsTest . NULL_TO_STRING_LIST ) ) ; assertEquals ( "abc" , StringUtils . join ( new String [ ] { "a" , "b" , "c" } ) ) ; assertEquals ( "a" , StringUtils . join ( new String [ ] { null , "a" , "" } ) ) ; assertEquals ( "foo" , StringUtils . join ( StringUtilsTest . MIXED_ARRAY_LIST ) ) ; assertEquals ( "foo2" , StringUtils . join ( StringUtilsTest . MIXED_TYPE_LIST ) ) ; } @ Test public void testJoin_ArrayCharSeparator ( ) { } @ Test public void testJoin_ArrayOfChars ( ) { } @ Test public void testJoin_ArrayOfBytes ( ) { } @ Test public void testJoin_ArrayOfInts ( ) { } @ Test public void testJoin_ArrayOfLongs ( ) { } @ Test public void testJoin_ArrayOfFloats ( ) { } @ Test public void testJoin_ArrayOfDoubles ( ) { } @ Test public void testJoin_ArrayOfShorts ( ) { } @ Test public void testJoin_ArrayString ( ) { } @ Test public void testJoin_IteratorChar ( ) { } @ Test public void testJoin_IteratorString ( ) { } @ Test public void testJoin_IterableChar ( ) { } @ Test public void testJoin_IterableString ( ) { } @ Test public void testSplit_String ( ) { } @ Test public void testSplit_StringChar ( ) { } @ Test public void testSplit_StringString_StringStringInt ( ) { } private void innerTestSplit ( final char separator , final String sepStr , final char noMatch ) { } @ Test public void testSplitByWholeString_StringStringBoolean ( ) { } @ Test public void testSplitByWholeString_StringStringBooleanInt ( ) { } @ Test public void testSplitByWholeSeparatorPreserveAllTokens_StringStringInt ( ) { } @ Test public void testSplitPreserveAllTokens_String ( ) { } @ Test public void testSplitPreserveAllTokens_StringChar ( ) { } @ Test public void testSplitPreserveAllTokens_StringString_StringStringInt ( ) { } private void innerTestSplitPreserveAllTokens ( final char separator , final String sepStr , final char noMatch ) { } @ Test public void testSplitByCharacterType ( ) { } @ Test public void testSplitByCharacterTypeCamelCase ( ) { } @ Test public void testDeleteWhitespace_String ( ) { } @ Test public void testLang623 ( ) { } @ Test public void testReplace_StringStringString ( ) { } @ Test public void testReplacePattern ( ) { } @ Test public void testRemovePattern ( ) { } @ Test public void testReplace_StringStringStringInt ( ) { } @ Test public void testReplaceOnce_StringStringString ( ) { } @ Test public void testReplace_StringStringArrayStringArray ( ) { } @ Test public void testReplace_StringStringArrayStringArrayBoolean ( ) { } @ Test public void testReplaceChars_StringCharChar ( ) { } @ Test public void testReplaceChars_StringStringString ( ) { } @ Test public void testOverlay_StringStringIntInt ( ) { }

Fix:
assertEquals ( "" , StringUtils . join ( new Object [ 0 ] ) ) ;